1. Field of the Invention
The present invention relates to a magnetic head and a magnetic recording/reproducing apparatus and, more particularly, to a magnetic head employing a magnetoresistive effect and a magnetic recording/reproducing apparatus equipped with such magnetic head.
2. Description of the Prior Art
In a magnetic disk drive, magnetic information are written/read into/from a magnetic disk by virtue of the magnetic head.
As shown in FIG. 13, for example, the magnetic head installed in the magnetic disk drive has such configuration a that both a magnetoresistive (MR) head 110 and an induction type head 120 are placed on a head substrate 101. In this configuration, the induction type head 120 is used to record the magnetic information into the magnetic disk, and the MR head 110 is used to reproduce the magnetic information from the magnetic disk.
A configuration as illustrated in FIGS. 14A and 14B and FIG. 15 has been employed as the MR head 110. FIG. 14A shows a planar placement of respective layers of the MR head 110 other than nonmagnetic insulating layers. FIG. 14B shows a layer structure of the MR head 110 except for the nonmagnetic insulating layers. FIG. 15 shows an end surface of the MR head 110, wherein a portion encircled with a broken line corresponds to a portion encircled with a broken line in FIG. 14B.
In FIGS. 14A, 14B and 15, a substrate protection insulating layer 102 is formed on a head substrate 101. Then, a lower magnetic shielding layer 111, a lower nonmagnetic insulating layer 112, a magnetoresistive device 113, an upper nonmagnetic insulating layer 114, and an upper magnetic shielding layer 115 are formed on the substrate protection insulating layer 102.
The magnetoresistive device 113 is formed to have a three-layered structure consisting of, for example, a soft magnetic layer, a magnetic separating layer, a magnetoresistive layer made of NiFe. First and second hard magnetic layers are formed respectively on both sides of the three-layered structure. Both the first and second hard magnetic layers are magnetized along the direction from the first hard magnetic layer to the second hard magnetic layer. First and second leads 116, 117 are formed between the lower nonmagnetic insulating layer 112 and the upper nonmagnetic insulating layer 114 and are connected to both sides of the magnetoresistive device 113 respectively.
In such a magnetoresistive head 110, when a sense current (constant current) is supplied to the magnetoresistive device 113 via the first and second leads 116, 117, a change in the electric resistance caused by a change in the magnetization direction by an external magnetic field is transmitted to a signal processing circuit (not shown) via the first and second leads 116, 117. Such change in the electric resistance appears as a change in voltage between the first and second leads 116, 117.
Accordingly, the first and second leads 116, 117 formed on both sides of the magnetoresistive device 113 have a function of supplying the sense current to the magnetoresistive device 113 and a function of applying a detected voltage.
The first and second leads 116, 117 are formed to have sufficiently large areas and thicknesses but small electric resistivity rather than the magnetoresistive device 113. For this reason, a total sum of the electric resistance of the first and second leads 116, 117 and the magnetoresistive device 113 can be substantially determined by the electric resistance value of the magnetoresistive device 113. Such electric resistance is set to about 20 to 40.OMEGA..
In FIG. 13, a reference numeral 105 denotes a magnetic disk.
The magnetoresistive magnetic head having the above configuration, before being mounted on a magnetic disk drive, is easily destroyed by static electricity. Reasons for this phenomenon will be put forth in the following.
First, when large static electricity is applied to the first lead 116, the static electricity moves from the first lead 116 toward the second lead 117 due to their potential difference, as indicated by an arrow I in FIG. 14A. In this event, the static electricity passes through the magnetoresistive device 113 as an electric route, and therefore the magnetoresistive device 113 becomes easily destroyed by the static electricity since it has larger electric resistance than the two leads 116, 117.
Then, as shown in FIG. 15, since the first and second leads 116, 117 and the lower and upper magnetic shielding layers 111, 115 may serve as electrodes while the lower and upper nonmagnetic insulating layer 112, 114 may serve as dielectric substances between them, parasitic capacitances may be formed. If the static electricity that is larger than an allowable value of the parasitic capacitance is accumulated between these electrodes, sometimes dielectric breakdown of the lower and upper nonmagnetic insulating layer 112, 114 may be caused by discharge of such static electricity. Discharging directions of the static electricity are indicated by arrows in FIG. 15.
In this manner, the reason why the static electricity enters into the first and second leads 116, 117 is that at first the static electricity enters into electrode pads (not shown) which are arranged on the magnetic head to be exposed to the outside, and then the static electricity moves to the first and second leads 116, 117 via wirings which are connected to the electrode pads.
As has been shown in Figures of Patent Application Publication (KOKAI) 6-243434, it may be thought out that a resistive film is coated on overall exposed ends of the magnetoresistive device in the magnetoresistive magnetic head, and then the leads are connected to the lower and upper magnetic shielding layers via the resistive film. However, according to such configuration, the static electricity accumulated in the leads is always discharged to the resistive film via the magnetoresistive device. Hence, such configuration is not preferable since it is likely that the magnetoresistive device is destroyed upon discharge of the static electricity.